Electrolyte-controlled redox conductivity and n-type doping in poly(bis-EDOT-pyridine)s

We report the use of electrolyte variations as a means to actively control redox and n-type doping processes in pi-conjugated electroactive polyheterocycles. Specifically, a series of donor-acceptor bis-EDOT-pyridine polymers, poly [2,5-bi s-(2,3-dihydro-thieno[3,4-b] [1,4]dioxin-5-yl)-pyridine] (PBEDOT-Pyr) and poly[5,8-bis(3-dihydro-thieno[3,4-b][1,4]dioxin-5-yl)-2,3-diphenyl-pyrido[3,4-b]pyrazine (PBEDOT-PyrPyr(Ph)(2)), have been investigated. The use of soft, bulky cations, such as n-alkylammonium, allows true n-type doping to be observed in cyclic voltammetry, differential-pulse voltammetry, and in situ conductance experiments. Color changes are also observed upon conversion of the polymers from their neutral to reduced states. Hard, electrophilic cations, such as lithium and sodium, induce minimal current and conductivity responses for these polymeric systems. This "pinning" of the cation-anion pair causes a decrease in the electrochemical and conductivity response. Optical changes upon reduction are observed that are distinct from the n-alkylammonium salts, indicating the lack of charge carrier formation and illustrating that reductive processes are not indicative of true doping in simple electrochemical experiments.